Culturing Borrelia from a persistently-infected host is rarely rewarding due to slow growth of the pathogen, dissemination out of the bloodstream and residence within immune-privileged sites. Probably the most sensitive way to detect persistent pathogen is xenodiagnosis. Here, an uninfected vector (in this case, Ixodes ticks) feeds on a host and acquires the pathogen, which may otherwise be undetectable. We have successfully used xenodiagnosis for detection of persistent Borrelia burgdorferi spirochetes in Lyme disease research. We now aim to identify the chemoattractants in tick saliva that recruit B. burgdorferi to the site of tick feeding. We hypothesize that one or more molecules within tick saliva possess strong chemoattractant properties for B. burgdorferi. In order to identify and isolate the molecules responsible for chemoattraction between ticks and B. burgdorferi, we propose two specific aims. The 1st aim will be to optimize our model system of B. burgdorferi chemotaxis. We will collect saliva from adult I. scapularis ticks and perform 3 different chemotaxis assays (U-tube counting, migration through a filter, and time-lapse microscopy) using mammalian host-adapted B. burgdorferi. The 2nd aim will be to identify the molecule(s) responsible for the chemotactic properties of I. scapularis saliva towards B. burgdorferi. We will perform chemotaxis assays with fractionated I. scapularis saliva to identify and separate candidate molecules. Successful purification of a chemotactic molecule will lead to improved understanding of the transmission process. In addition, this chemoattractant could provide a minimally invasive but highly effective adjunct to testing for the presence of persistent spirochetes or treating infectio with antibiotics that may have reduced tissue penetration.